NOTES ON PLYMOUTH HYDROIDS. c 



peduncled hydrothecae, affords a good idea of how the fascicled 

 stems of hvdroids may have arisen. In some of the specimens 

 the aggregation of root-stalks would doubtless be sufficiently 

 rigid to support themselves in an erect position after the stem to 

 which they cling had died, and we should then have a loosely 

 put together, fascicled stem, which a little further differentia- 

 tion would convert into a typical polysiphonic hydrocaulus. 



The tubular extension of the hydrothecas reminds one of 

 similar structures in the genus Crxftolaria. which contains 

 several species further related to the one under discussion, in 

 having the operculum composed of convergent segments. 



Cuspidella grandis Hincks. In looking over my Ply- 

 mouth series of hvdroids after returning to America. I found 

 specimens of this species growing over the stems of Halecium 

 tenellum. A careful examination of the stems of the larger 

 hvdroids is frequently repaid by the discovery of one or more 

 species of minute parasitic forms which escape the casual 

 observer, and it is quite likely that a number of new species 

 would reward the patience of any one who would devote him- 

 self for a time to a search for these forms on British coasts. 



Halecium tenellum Hincks. A number of colonies with 

 female gonangia were taken from a depth of iS fathoms on 

 April 19th. These specimens closely resemble in several 

 points miniature colonies of H. labrosum Alder, especially in 

 the shape of the gonangia and the wrinkled appearance of the 

 stems, which, however, are monosiphonic. Indeed, one can- 

 not wonder that Alder mistook //. tcncdum for the young of 

 H. labrosum. Out of a large number of colonies of H. tenel- 

 lum from Plymouth, there are none over half an inch in 

 height, and they very generally show the reduplication of the 

 margins of the hvdrophores, which Hincks mentions as a char- 

 acteristic feature. 



Plumularia pinnata Linn. This is by far the most 

 abundant Plumularian at Plymouth, and afforded an excellent 

 opportunitv to study the morphology and reproduction of the 

 group. 



